rotateZ() not working as expected

Processing Development
3

Hello,

My accelerometer only had x, y and z and I did not use the “yaw” axis which is perpendicular to gravity and was not useful in this case; I would have needed another accelerometer mounted at 90 deg for this axis.
I included some code that uses scrollbar to rotate a shape using intrinsic Euler angles for yaw, pitch and roll; see mapping in scrollbar code (this could have been moved).
Some videos I made for other projects below (code not included) that only used two of the axes.
Android to Processing demo:
https://www.youtube.com/watch?v=oyuA0aiQ7tM
Arduino to Processing:
https://www.youtube.com/watch?v=dMURX-00Hyg

// GLV
// 2018-06-10
// Scrollbar control of Euler angles for pitch, yaw and roll
// https://en.wikipedia.org/wiki/Euler_angles
// https://en.wikipedia.org/wiki/Aircraft_principal_axes
// Using intrinsic rotations are elemental rotations that occur about the axes of a coordinate system XYZ attached to a moving body. 
// Processing co-ordiante system not changes for this example.

float x, y, z;

boolean control = true;
  
void setup() 
  {
//scrollbar
  hs1 = new HScrollbar(width/4, 57*height/64, width/2, 10, 10);
  hs2 = new HScrollbar(width/4, 59*height/64, width/2, 10, 10);
  hs3 = new HScrollbar(width/4, 61*height/64, width/2, 10, 10);
 
// Scrollbar defaults
  hs1.setPos(width/2);
  hs2.setPos(width/2);
  hs3.setPos(width/2);         
    
  size(800, 1000, P3D);
  textAlign(CENTER, CENTER);
  textSize(36);
//  ortho();
  }

void draw() 
  {
  background(0);   
  lights();
 
// Scrollbars
  fill(255);
  textSize(24);
  textAlign(RIGHT, BOTTOM);
  text("Pitch X",   width/4-50, 57*height/64 +15);
  text("Yaw Y",     width/4-50, 59*height/64 +15);
  text("Roll Z",    width/4-50, 61*height/64 +15);
  
  hs1.update();
  hs2.update();
  hs3.update();  
  hs1.display();
  hs2.display();
  hs3.display();  
  
  translate(width/2, height/2);

  if (control)
    {
    x = hs1.getPos4();
    y = hs2.getPos4();
    z = hs3.getPos4();
    plotScroll(x, y, z);
    }
  }


// Axes
float length = 200;

void drawAxes1()
  {
// X axis
  stroke(255);
  strokeWeight(3);
  fill(255, 255, 0);
  
  line(-length, 0, 0, length, 0, 0);
  text("X", length+60, 0, 0);
  text("-X", -length-60, 0, 0);

// Y axis  
  line(0, -length, 0, 0, length, 0);    
  text("Y", 0, length+60, 0);
  text("-Y", 0, -length-60, 0);

// Z Axis
  line(0, 0, -length, 0, 0, length);   
  text("Z", 0, 0, length+60);
  text("-Z", 0, 0, -length-60);  
  }
  
// Plot from scroll bar
public void plotScroll(float x, float y, float z)
  {
 pushMatrix();
// Processing has a LHS of coordinates
  rotateX(x);           // Pitch
  rotateY(y);           // Yaw 
  rotateZ(z);           // Roll
  fill(100, 255, 0);    
  strokeWeight(1);
  box(200, 10, 500);    
  drawAxes1();
 popMatrix();
  }

// From Processing examples. Modified.

HScrollbar hs1, hs2, hs3;  // Create 3 scrollbars

class HScrollbar 
  {
  int swidth, sheight;    // width and height of bar
  float xpos, ypos;       // x and y position of bar
  float spos, newspos;    // x position of slider
  float sposMin, sposMax; // max and min values of slider
  int loose;              // how loose/heavy
  boolean over;           // is the mouse over the slider?
  boolean locked;
  float ratio;

  HScrollbar (float xp, float yp, int sw, int sh, int l) 
    {
    swidth = sw+10;
    sheight = sh;
    int widthtoheight = sw - sh;
    ratio = (float)sw / (float)widthtoheight;
    xpos = xp;
    ypos = yp-sheight/2;
    spos = xpos + swidth/2 - sheight/2;
    newspos = spos;
    sposMin = xpos;
    sposMax = xpos + swidth - sheight;
    loose = l;
    }

  void update() 
    {
    if (overEvent()) 
      {
      over = true;
      } 
    else 
      {
      over = false;
      }
    if (mousePressed && over) 
      {
      locked = true;
      }
    if (!mousePressed) 
      {
      locked = false;
      }
    if (locked) 
      {
      newspos = constrain(mouseX-sheight/2, sposMin, sposMax);
      }
    if (abs(newspos - spos) > 1) 
      {
      spos = spos + (newspos-spos)/loose;
      }
    }

  float constrain(float val, float minv, float maxv) 
    {
    return min(max(val, minv), maxv);
    }

  boolean overEvent() 
    {
    if (mouseX > xpos && mouseX < xpos+swidth && mouseY > ypos && mouseY < ypos+sheight) 
      {
      return true;
      } 
    else 
      {
      return false;
      }
    }

  void display() 
    {
    noStroke();
    fill(204);
    rect(xpos, ypos, swidth, sheight);
    if (over || locked) 
      {
      fill(0, 0, 0);
      } 
    else 
      {
      fill(102, 102, 102);
      }
    rect(spos, ypos, sheight, sheight);
    }

  float getPos() 
    {
    // Convert spos to be values between and total width of the scrollbar
//    println(spos);
    return spos * ratio;                    
    }
    
  float getPos4() 
    {
    // Convert spos to be values between 0 and the total width of the scrollbar
    println(spos);
    float spostmp = map(spos, width/4, width/2 + width/4, -TAU/4, TAU/4);
    return spostmp;
    } 

// GV Added to setPos
  void setPos(float pos) 
    {
    // Convert spos to be values between
    spos = pos;
    newspos = pos;
    }
  }
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